Upload
harpreet-singh
View
268
Download
6
Embed Size (px)
Citation preview
8/10/2019 Final Classification of Soil PPT
1/35
Classification Of Soil
Gurdarshan Singh
Roll no 1307Geotechnical Engineering
8/10/2019 Final Classification of Soil PPT
2/35
1.Purpose
Main soils are ;clay, silt, sand, gravels andboulders etc.
Above type seldomexits separately in the
nature.
Natural soil deposits comprise mixture of
above type in varies proportions.
Soil classification mean to arrange in soil of
groups and label them based on theirproperties and behavior.
Soil classification has been developed by
different organizations .
8/10/2019 Final Classification of Soil PPT
3/35
8/10/2019 Final Classification of Soil PPT
4/35
. Classifying soil into groups with similar behavior into the termof Simple indices can provide geotechnical a general guidance
about engineering properties of the soil through theaccumulated of experiences .
Communicate
between
Engineers
Simple index Classification Estimate Achieve
system Engineering Engineering
GSD, LL, PL ( Language ) Properties Purposes
Use the
accumulated
experience
8/10/2019 Final Classification of Soil PPT
5/35
Soil Classification System
Classification system developed by different organization
1 Unified Soil Classification System (USCS).
2 AASHTO ( American Association Of State Highway and
Transportation official ) soil classification .
3 Indian Standard Classification System (ISCS)
8/10/2019 Final Classification of Soil PPT
6/35
1. Unified Soil Classification
System(USCS)
The Unified Soil Classification System (USC) was first
developed by casagrande in 1948. It is modified by the Bureau of Reclamation and the crops of
Engineers of the Unified State of America.
The system has also been adopted by American Society of
Testing Material (ASTM). The System is the most popular system for use in all types of
engineering problems involving soils .
8/10/2019 Final Classification of Soil PPT
7/35
There are four major divisions of unified soil classification system
(USCS)
(1) Coarse Grained
(2) Fine-Grained
(3) Organic Soils
(4) Peat
8/10/2019 Final Classification of Soil PPT
8/35
Definition of Grain Size
8
Boulders Cobbles
Gravel Sand Silt and
Clay
Coarse Fine Coarse FineMedium
300 mm 75 mm
19 mm
No.4
4.75 mm
No.10
2.0 mm
No.40
0.425 mm
No.200
0.075mm
No specific grain
size-use
Atterberg limits
8/10/2019 Final Classification of Soil PPT
9/35
General Guidance
9
Coarse-grained soils:
Gravel Sand
Fine-grained soils:
Silt Clay
NO.200
0.075
mm
Grain size distribution
Cu
Cc
PL, LL
Plasticity chart
50 %
NO. 44.75 mm
Required tests: Sieve analysis
Atterberg limit
LL>50 LL
8/10/2019 Final Classification of Soil PPT
10/35
Dry Clay Silt Medium Coarse Sand Fine Gravel Medium Gravel
Sieve Analysis
8/10/2019 Final Classification of Soil PPT
11/35
Liquid Limit (LL) Test
Plastic Limit Device
PlasticLimit(PL)
Atterberg Limits
(Standard tests methods
for Liquid Limit, Plastic
Limit and Plastic Index of
properties)
8/10/2019 Final Classification of Soil PPT
12/35
Symbols
12
8/10/2019 Final Classification of Soil PPT
13/35
8/10/2019 Final Classification of Soil PPT
14/35
8/10/2019 Final Classification of Soil PPT
15/35
Procedures for Classification
15
Coarse-grained
material
Grain size
distribution
Fine-grained
material
LL, PI
Highly
8/10/2019 Final Classification of Soil PPT
16/35
Organic Soils
Highly organic soils- Peat (Group symbol PT)
A sample composed primarily of vegetable tissue in various stages of
decomposition and has a fibrous to amorphous texture, a dark-
brown to black color, and an organic odor should be designated as a
highly organic soil and shall be classified as peat, PT.
Organic clay or silt( group symbol OL or OH):
Thesoils liquid limit (LL) after oven drying is less than 75 % of its
liquid limit before oven drying.If the above statement is true, then
the first symbol is O.
The second symbol is obtained by locating the values of PI and LL
(not oven dried) in the plasticity chart.
16
8/10/2019 Final Classification of Soil PPT
17/35
17
Borderline Cases (Dual Symbols)
For the following three conditions, a dual symbol should be used. Coarse-grained soils with 5% - 12% fine.
About 7 % fines can change the hydraulic conductivity of the
coarse-grained media by orders of magnitude.
The first symbol indicates whether the coarse fraction is well or
poorly graded. The second symbol describe the contained fines. Forexample: SP-SM, poorly graded sand with silt.
Fine-grained soils with limits within the shaded zone. (PI between 4
and 7 and LL between about 12 and 25).
It is hard to distinguish between the silty and more claylike
materials.
CL-ML: Silty clay, SC-SM: Silty, clayed sand.
Soil contain similar fines and coarse-grained fractions.
possible dual symbols GM-ML
8/10/2019 Final Classification of Soil PPT
18/35
18
Borderline Cases (Summary)
2 A i A i ti Of St t
8/10/2019 Final Classification of Soil PPT
19/35
2. AmericanAssociation Of StateHighway And Transportation
Official System
This system was originally developed by Hogentogler and
Terzaghi in 1929 as the public roads classification system .
They particle size analysis and the plasticity characteristics
are required to classify a soil .
The classification system is a complete system which classifies
both the coarse grained and fine grained soils.
8/10/2019 Final Classification of Soil PPT
20/35
The system is based on the following three soil properties:
1.Particle-size distribution .
2.Liquid Limit .
3.Plasticity Index .
8/10/2019 Final Classification of Soil PPT
21/35
Key Elements:
1.Grain Size:
Gravel: Fraction passing 75mm sieve and retained on #10 (2mm)US sieve
Sand: Fraction passing #10 sieve and retained #200 sieve
Silt and Clay: Fraction passing #200 sieve
2.Plasticity:
Term silty is applied when fine fractions have a PI< 10
Term clayey is applied when fine fractions have PI> 11
3.Groups:
Soilsareclassifiedintoeightgroups,A-1throughA-8.
ThemajorgroupsA-1,A-2,andA-3representthecoarsegrainedsoils.
TheA-4,A-5,A-6,andA-7representfinegrainedsoils.
TheA-8areidentifiedbyvisualinspection.
8/10/2019 Final Classification of Soil PPT
22/35
The ranges of the LL and PI for groups A-2,A-4,A-5,A-6andA-7:
8/10/2019 Final Classification of Soil PPT
23/35
General Guidance 8 major groups: A1~ A7 (with several subgroups) and organic
soils A8
The required tests are sieve analysis and Atterberg limits.
The group index, an empirical formula, is used to furtherevaluate soils within a group (subgroups).
The original purpose of this classification system is used for roadconstruction (sub grade rating).
A4 ~ A7A1 ~ A3
Granular Materials
35% pass No. 200 sieve
Silt-clay Materials
36% pass No. 200 sieve
Using LL and PI separates silty
materials from clayey materials
Using LL and PI separates silty
materials from clayey materials(only for A2 group)
8/10/2019 Final Classification of Soil PPT
24/35
24
Group Index
)10PI)(15F(01.0
)40LL(005.02.0)35F(GI
200
200
)10PI)(15F(01.0GI 200
For Group A-2-6 and A-2-7
The first term is determined by the LL
The second term is determined bythe PI
In general, the rating for a pavement sub grade is
inversely proportional to the group index, GI.
use the second term
only
F200: percentage passing through the No.200 sieve
8/10/2019 Final Classification of Soil PPT
25/35
It may be noted that:
The higher the value of GI the weaker will be the soil and
vice versa. Thus, quality of performance of a soils a sub grade
material is inversely proportional to GI.
A soil having GI of zero is considered as the best.
If the equation gives negative value for GI, consider it zero.
Always round off the G I to nearest whole number.
GI=0 for soils of groups A-1- a, A-1-b ,A-2- 4, A-2-5, and A-3.
For groups A-2-6 and A-2-7 use partial GI for PI only:
8/10/2019 Final Classification of Soil PPT
26/35
Classification of Highway Subgrade Materials :
8/10/2019 Final Classification of Soil PPT
27/35
Classification of Highway Sub grade Materials :
8/10/2019 Final Classification of Soil PPT
28/35
Indian Standard Classification System
(ISC)
Indian standard classification (ISC) system adopted by bureau
of Indian standards is in many respects similar to the Unified
Soil Classification (UCS) system.
There is one basic difference in the classification of fine
grained soils .
The fine grained soils in ISC system are subdivided into three
categories of low, medium and high compressibility instead of
two categories of low and high compressibility in USC system .
8/10/2019 Final Classification of Soil PPT
29/35
Soils are divided into three broad divisions :
1. Coarse grained soils, when 50% or more of the total material
by weight is retained on 75 micron IS sieve .
2. Fine grained soils, when more than 50% of the total materialpasses 75 micron IS sieve .
3. If the soil is highly organic and contains a large percentage of
organic matter and particles of decomposed vegetation, it iskept in a separate category marked as peat (Pt).
8/10/2019 Final Classification of Soil PPT
30/35
Basic Soil Components in ISC System1. Coarse grained soils Coarse grained soils are sub divided
onto gravel and sand. The soil is termed gravel(G) whenthan 50% of coarse fraction (plus 75) is retained on 4.75mm IS sieve , and termed sand (S) more than 50% of thecoarse fraction is smaller than 4.75 mm IS sieve.
2. Fine grained soils the fine grained soils are further dividedinto three subdivisions, depending upon the values of theliquid limit:
a) Silts and clays of low compressibility these soils have aliquid limit less than 35.
b) Silts and clays of medium compressibility these soils have aliquid limit greater than 50.
c) Silts and clays of high compressibility- these soils have aliquid limit greater than 50.
8/10/2019 Final Classification of Soil PPT
31/35
Basics Soil Components ISC System
8/10/2019 Final Classification of Soil PPT
32/35
8/10/2019 Final Classification of Soil PPT
33/35
8/10/2019 Final Classification of Soil PPT
34/35
Reminder 0.075 mm(75m) separates coarse and fine grained soils .
Uniformly graded soils are poorly graded .
Grain size distributions are mainly for coarse grained soils;Atterberg limits are for fines.
Clay particles are negatively charged flakes with a high surface
area and are smaller than 2m in size; they are plastic andsticky (cohesive). Silts are non plastic (PI=0)
A fine grained soil is classified as clay or silt based onAtterberg limits not on relative proportions .
The first thing one should know when classifying a soil is the% of fines.
In AASHTO, the general rating as a subgrade decreases fromleft to right, A-1 being the best and A-8 being the worst.
8/10/2019 Final Classification of Soil PPT
35/35
References
Soil Mechanics And Foundation Engineering ( DR. K.R. Arora).
Geotechnical Engineering ( N Sivakugan / Braja M. Das).
Soil Mechanics and Foundations ( Dr B C Punmia and Ashok
Kumar Jain)